Lactic acid, which can be produced chemically or biologically, is a widely used chemical compound that ranges from use in the cosmetic industry to use in the food industry to the pharmaceutical and chemical industries. Since lactic acid contains two reactive functional groups, a carboxylic group and a hydroxyl group, it can undergo a variety of chemical conversions into potentially useful chemicals, such as propylene oxide, acetaldehyde, acrylic acid, propanoic acid, 2,3-pentanedione, and lactide (Varadarajan and Miller, Biotechnol. Progr. 15:845, 1999). Recently, increased attention has been directed at the use of lactic acid to produce polylactic acid (PLA), which is a renewable raw material used in the manufacture of bioplastics that offers a more sustainable alternative to petrochemical resources. Optically pure lactic acid can be polymerized into a high molecular mass PLA through the serial reactions of polycondensation, depolymerization, and ring-opening polymerization (Södergård and Stolt, Prog. Polym. Sci. 27:1123, 2002). The resultant PLA polymer has various uses in wide ranging applications, including protective clothing, food packaging, mulch film, trash bags, rigid containers, shrink wrap, and short shelf-life trays (Drumright et al., Adv. Mater. 12:1841, 2000; Vink et al., Polym. Degrad. Stabil. 80:403, 2003).
The carbohydrate feedstocks currently used in biological lactate production are relatively expensive. Other feedstocks, such as methane, are available cheaply in large quantities. The conversion of methane potentially represents a route to significantly lower cost lactic acid production. However, a practical way of achieving this has not yet been developed.